This invention relates to a process and apparatus applicable where an aqueous solvent is to be recovered by multiple effect evaporation with the simultaneous recovery of solute, and more particularly, where a miscella obtained by the extraction of defatted seed material with organic carbohydrate-selective extraction solvent is to be separated by multiple effect evaporation and stripping into recovered solvent and solute dissolved in water free of said organic constituent.
Oleaginous seed materials, such as soybeans, cottonseeds, peanuts, sesame seeds, and sunflower seeds contain high concentrations of nutritious proteins. Other constituents are fiber, oil and carbohydrates. Since the carbohydrates are often associated with characteristic undesirable flavors and since they are also the cause of flatulence when the untreated seeds are used in a human diet, it is known to extract flaked seeds first with a solvent, such as hexane, to remove the oil content and then to extract the defatted flakes with a carbohydrate-selective solvent, to leave as the residue a protein concentrate. One class of carbohydrate-selective solvents known to the art is aqueous solutions of low boiling alcohols, such as methanol, ethanol, and isopropanol.
A complete carbohydrate extraction process necessarily includes an extraction step, a spent flakes desolventizing step, and a miscella evaporation step. Such a process employing aqueous alcohol for the extraction of defatted seed material, such as soybean flakes, is exemplified by the disclosure of co-pending application Ser. No. 371,148 filed June 18, 1973, assigned to the same assignee as the present invention. Extraction is carried out in a series of stages, each stage comprising in sequence contacting solvent and solids, separating the phases, and expressing the wet solid to further reduce the solvent retained therein. Flow of solvents and solids in each stage is concurrent; but flow of solids and solvent between stages is countercurrent. Expressed solids from the extractor are desolventized by heating and are then stripped of residual alcohol by contacting with steam or other inert gas. Miscella is evaporated to recover solvent while simultaneously recovering the extracted carbohydrates as a syrup in aqueous solution which has been stripped free of alcohol. It is the evaporation and stripping step that is the subject of this invention.